A recent study by the Animal Protection Institute showed that even with windows slightly open, 85-degree outdoor temperatures translate to 102 degrees inside a car within 10 minutes and 120 degrees within half an hour.

Potts said most people don’t realize how warm their cars get in the summer, so they often leave a pet or child unattended while running short errands.

Parking in the shade can help. But dogs cool down by breathing cool air, and the shade only makes the air less hot, not cool, she said.

So Potts wants signs all over the county warning people of the dangers and reminding them that California has criminal penalties for such behavior.

“Like with smoking and seat belts, we change and learn through education,” she said.

If people see a child or pet trapped in a warm car, they should dial 911, she said.

Potts launched her campaign last September by lobbying the Escondido City Council to post warning signs in municipal parking lots.

City officials embraced the concept and then approved the signs for all private lots. But they haven’t OK’d them for municipal lots.

Barbara Redlitz, the city’s planning chief, said that one issue needing exploration would be who pays for maintaining the signs and replacing them when they decay.

Redlitz said officials would accelerate the process if the City Council directed them. Potts said she plans to lobby the council again this spring.

Media coverage of her efforts in Escondido last fall allowed Potts to form partnerships with the Escondido Humane Society, which came up with the sponsorship idea, and nonprofit San Diego Animal Advocates in Encinitas.

Jane Cartmill, director of that organization, said she’s working with the Encinitas City Council on similar requests.

“Every summer we constantly see an awful lot of dogs in cars,” she said. “People think they’ll only be gone for a minute, but it ends up being longer. We hope this campaign is going to catch on.”

Cartmill’s organization paid for 10 of the 17 signs installed last week by Ace. Three signs were sponsored by Sally Costello, executive director of the Escondido Humane Society, and the others were funded by individuals.

Potts said they cost about $55 each, but that the price could fall with a bulk order.

Kristin Ludwick, an Ace Parking spokeswoman, said this week that company officials immediately embraced Potts’ campaign and that Ace might expand it outside San Diego.